1. Field of the Invention
The invention relates to logistic-fueled direct energy conversion power sources, such as thermophotovoltaic (TPV), thermoelectric (TE), and alkali-metal-thermal-to-electric-conversion (AMTEC) devices, and is directed more particularly to a burner and a bumer/emitter/recuperator (BER) assembly for use in such power sources.
2. Description of the Prior Art
Two major components of a direct energy conversion power source are (1) a burner/emitter recuperator (BER) assembly, and (2) a power converter assembly (PCA). The objective of the BER is to burn fuel cleanly with the lowest amount of parasitic power consumption and to convert the highest fraction of combustion energy in the fuel to radiant thermal energy. Logistic fuels, as defined by the U.S. military, include diesel (DF-2) and JP-8, and have been preferred inasmuch as they provide the advantages of high energy density and transportability. The PCA converts the radiant thermal energy directly into electrical power through thermophotovoltaics (TPV), thermoelectric (TE), or alkali-metal-thermal-to-electric-conversion (AMTEC).
For small power sources with high system efficiencies, the fuel-firing rate is very low. For instance, a 250 W.sub.e power source with a system efficiency of 10% (fuel to electric power) has a fuel firing rate of only 0.07 gallons per hour. To achieve 10% or higher efficiency, the combustion air has to be preheated to a temperature of at least 2000.degree. F. The combination of logistic fuel, very low fuel firing rate, and very high air preheat temperature makes the burner design extremely challenging. The conventional pressure-atomized retention head burners cannot be used for such low fuel firing rates because of the extremely small orifice size involved. Other advanced burner designs for low fuel firing rates, such as ultrasonic atomization burners, electrostatic atomization burners, air atomized burners, vaporizing burners, and Babington atomizers have their own unique problems for this application, mostly resulting from extremely high air preheat temperature (about 2000.degree. F.), super high flame temperature (about 4000.degree. F.), or very high combustion chamber temperature (about 3000.degree. F.). For example, the very high temperature of the combustion air causes "coking" of the burner nozzle outlet, i.e. accumulation of fuel residues which, because the orifices are extremely small, leads to blockage of orifices, malfunctioning of the burner, and breakdown of the power assembly.
There is thus a need for a burner and a burner/emitter/recuperator (BER) assembly for power converters, which burner and assembly uses logistic fuel with very high temperature combustion air, produces a high flame temperature, maintains a high combustion temperature, and has the following features:
Does not suffer from fuel coking; PA1 Has smooth ignition without smoke or unburned hydrocarbon emissions; PA1 Provides precise fuel flow regulation; PA1 Can operate at very low ambient temperatures; and PA1 Has low parasitic power requirements.